CSET 118: Tectonic Processes and Features

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CSET 118: Tectonic Processes and Features
2013-06-30 11:47:43

Science CSET
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  1. What is the evidence that supports continental drift
    • the fit of the continents 
    • fossils of extinct late paleozoic plant and animal species are found on widely separated continents 
    • evidence of the location of global climatic belts 
    • evidence from mountain ranges and rock types
    • paleomagnetism - magnetic minerals in basalt that line up with the Earth's magnetic field are frozen in place as the lava flow cools, recording the location of the planet's magnetic north pole at the time it formed
  2. Diagram the features that provide evidence for plate tectonics
    • bathymetry - seafloor has enormous mountain ranges named mid-ocean ridges, deep trenches, huge fractures and some flat plains 
    • paleomagentism on the ocean floor - zebra stripes of different paleomagnetic polarity, sometimes the magnetic poles switch
    • ages of rocks of the ocean floor - ocean rocks go rock youngest at the mid-ocean ridges to oldest at the farthest points from the ridges 
    • seafloor spreading - the mechanism for moving continents, the creation of new seafloor and the spreading of old seafloor away from the ridge axis 
    • convection currents - mantle convection drives seafloor spreading
    • plate tectonics = continental drift + seafloor spreading
  3. Summarize the thermal processes driving plate movement
    • mantle convection - convection cells form in the Earth's mantle
    • the source of heat is the Earth's core which warms the lower layer of the mantle which rises to the top of the mantle then spreads outward in both directions beneath the crust 
    • the material cools eventually becoming negatively buoyant and sinking, traveling back to the lower layer of the mantle to be warmed again 
    • upwelling mantle material rises beneath the mid-ocean ridges -> the ridges have high heat flow -> makes them buoyant and they stand higher than the surrounding ocean floor 
    • heat causes the upper mantle to melt -> produces basalt lavas that erupt at the mid-ocean ridge -> creates new ocean crust 
    • the mantle material spreads outward in both directions from the mid-ocean ridge carrying the oceanic crust with it, mantle cools as it moves further from its heat source 
  4. Explain how density and buoyancy are related to plate tectonics
    • if temperature of fluid rises, molecules move more vigorously and take up more space, since mass hasn't changed the density decreases 
    • lower density means warmed fluid has greater buoyancy than the fluid around it and rises
    • if the buoyancy fore on an object is equal to the force of gravity the object has neutral buoyancy
    • lithosphere - crust and uppermost mantle
    • asthenosphere - mantle just below the lithosphere 
    • oceanic crust - thinner and denser
    • continental crust - less dense but much thicker and more buoyant 
    • isostasy - the Earth's lithosphere floats on the denser asthenospere
    • both oceanic and continental lithosphere are less dense than the mantle beneath them and are more buoyant so they "float" on the mantle 
    • when two slabs of lithosphere come together, what happens depends on their relative densities - the denser slab will sink beneath the less dense slab or if two continental lithospheres meet they are so buoyant neither will sink
  5. Describe types of plate boundaries
    • convergent boundary - plates move toward each other 
    • two oceanic plates converge to create a subduction zone 
    • when two oceanic plates collide, the denser of the plates plunges beneath the other in subduction
    • a continental and oceanic plate converge to create a subduction zone - the oceanic plate subducts beneath the continental plate 
    • partial melting of the subducting plate may form a chain of volcanoes 
    • two continental plates converge to create a mountain range 

    • divergent boundary - plates move apart
    • spreading ridges where seafloor spreading occurs
    • new ocean crust forms as the plates move away from each other  

    • transform boundary - plates slide past each other
    • plates move along faults - cracks in the crust 
    • earthquakes - plates move in big jolts
  6. Relate the causes of volcanoes, earthquakes, and earth resources to tectonic processes
    • earthquakes:
    • ⋄ most are caused by lithospheric plates moving against each other 
    • ⋄ when the stresses build up enough energy they overcome the frictional forces and the two pieces of crust slip past each other - the energy is released causing an earthquake 
    • ⋄ almost all earthquakes occur at all three types of plate boundaries
    • ⋄ plate boundaries have their own earthquake depths 

    • volcanoes:
    • ⋄ found at convergent and divergent boundaries - where mantle melts 

    • earth resources:
    • ⋄ metallic minerals are found in subduction zones - they form in and near magma chambers
    • ⋄ some magma bodies cool below the surface and form plutons which heat and supply fluids to the surrounding rock
  7. Summarize earthquake processes in terms of epicenter, focal mechanism, distance, and materials, and the role various factors play in the amount of damage caused by an earthquake
    • epicenter: position where the damage is greatest, point on Earth's surface directly above the focus - point in the crust where energy is released, use seismographs to determine 
    • focal mechanism: the amount of motion that rocks along the fault undergo and the orientation of the fault 
    • dip-slip faults: has vertical motion
    • - normal fault: the hanging wall goes down relative to the footwall 
    • - reverse fault: the hanging wall goes up relative to the footwall
    • - thrust fault: reverse fault in which the fault plane is at an angle less then 45 degrees
    • strike-slip fault: has only horizontal motion 
    • - left-lateral (sinistral) strike slip fault: left foot moves toward you 
    • - right-lateral (dextral) strike slip fault: right foot moves toward you 
    • seismic waves: how the energy released during an earthquake travels
    • - body waves:
    •    - P (primary) waves: fastest, compressional waves, can travel through any substance, causes structures to compress and expand which weaken and can collapse the building 
    •    - S (secondary) waves: travel in a side-to-side motion, only travel through solids, shake buildings 
    • - surface waves: travel at the interface between two different substances, much slower than body waves, roll along the surface like ripples and side-to-side, do significant damage because they are on the surface  
    •    - rayleigh and love waves 
    • factors determining damage:
    • strength and amplitude of the seismic waves
    • duration of shaking 
    • geology of the area